Electrode



Patented Dec. 5, 1922.

UNHTE COLIN G. FINK, OF YONKERS, NEW YORK, ASSIGNOR T0 CHILE EXPLORATIONCOM- PANY, OF NEW YORK, N. Y., ACOBPORATIGN OF NEW JERSEY.

ELECTRODE.

No Drawing.

To all whom, it may concern Be it known that I, COLIN G. FINK, a citizenof the United States, residing at Yonkers, in the county of estchester,State of New York, have invented certain new and useful Improvements inElectrodes; and I do hereby declare the following to be a full, clear,and exact description of the invention, such as will enable othersskilled in the art to which it appertains, to make and use the same.

This invention relates to an improved electrode of particular value foruse as an anode in the electro-deposition of copper from cop per sulfateelectrolytes, but available for use for other purposes.

For efiicient. and satisfactory use in the electrolytic recovery ofcopper from copper sulfate electrolytes, an anode should possess certainproperties. In the first place, it should be of the socalled insolubleanode type, that is to say, it should be to a high degree insoluble inthe electrolyte, or in other words, it should possess high resistance toanodic disintegration. In addition, the anode should have highelectrical conductivity and a low anodic potential in order to maintainthe electrical losses as low as practicable. And again, the anode shouldbe of such a character as to permit the ready dis charge of oxygen gastherefrom, therebty eliminating or minimizing the undesirableconsequences of polarization. In practice, it is generally only possibleto approximate the ideal condition with respect to each of theaforementioned properties, and, accordingly, it is necessary in theproduction of an anode for commercial practice to resort to a compromiseof the ideal conditions with respect to these proporties in order toobtain an anode possessing the desired properties to a more or lesssatisfactory degree.

The present invention contemplates the provision of an improved anodepossessing in a remarkably satisfactory degree the aforementioneddesirable properties. Thus, the anode of the invention is highlyresistant in anodic disintegration, and, in addition, has a low anodepotential and good .electrical conductivity. Moreover, in its preferredform, the anode possesses to a satisfactory Serial No. 353,103.

degree depolarizing characteristics permitting the free discharge ofoxygen gas from its surface.

In its broad aspect, the invention contemplates the provision, as a newarticle of manufacture, of an electrode resistant to anodicdisintegration andmade up of an alloy containing cobalt and silicon. Adepolarizing ingredient, such as manganese, is preferably included inthe alloy, and, as a result of electrolytic action, provides adepolarizing coating or film for the surface of the electrode whichfacilitates the discharge of oxygen gas therefrom. A hardening agent isalso preferably included in the alloy and serves the purpose ofhardening the surface coating or film of the depolarizing agent.Chromium may be advantageously used as the hardening agent, and I havefound that tungsten, molybdenum and uranium may also be used as thehardening agent. Throughout the specification and the appended claims, Ihave mentioned manganese with the intention of defining any equivalentdepolarizing ingredient and similarly I have mentioned chromium with theintention of defining any equivalent hardening agent.

The improved electrode of the invention is accordingly made up of analloy of which the principal constituents are cobalt and silicon. In itspreferred form, the electrode also contains manganese and chromium,together with a certain amount of carbon. I have secured excellentresults with an alloy of the following composition: 11.5 to 13% silicon,4 to 6% manganese, 1 to 6% chromium, 0.8 to 1.2% carbon, and the balancecobalt. If desired, 5 to 30 parts of the cobalt content of the alloy maybe replaced by manganese, or 5 to 12 parts of the cobalt content may bereplaced by chromium, or 5 to 8 parts of the cobalt content may bereplaced by nickel, Without objectionably altering the advantageousproperties of the alloy as an anode material.

As the result of my investigations and researches, I have found that animproved electrode, resistant to anodic disintegration in theelectro-deposition of copper from copper sulfate electrolytes, and inparticular, copper sulfate electrolytes containing chlorides andnitrates, can be produced from cobalt and silicon, by combining thesemetals in the form of a cobalt-silicon alloy of appropriate composition.I have also found that when cobalt and silicon are appropriately alloyedtogether with a small amount of manganese and carbon, the resultingalloy shows a marked resistance to such anodic disintegration and hasgreater strength and other desirable qualities which adapt itparticularly for use as an insoluble anode in the electrodeposition ofcopper from sulfate solutions. I have, moreover, found that the additionof chromium, or other equivalent metal of the chromium group such astungsten, molybdenum or uranium, to the alloy imparts to the electrodefurther advantageous characteristics which will be more particularly mentioned hereinafter.

I have found that commercial cobalt is well adapted for use in theproduction of electrodes in accordance with the principles of theinvention. Cobalt has a marked affinity for carbon and, if desired, maybe preliminarily combined with the amount of carbon to be incorporatedin the anode alloy. The proportion of carbon, of manganese, of chromium,and of silicon can be somewhat varied, but in general neither thecarbon, the manganese, the chromium or chromium group metal, nor thesilicon should be too low, or the corrosion of the anode will beobjectionably increased. On

the other hand, the carbon, the manganese, the chromium and the siliconcontent should not be too high. A highsilicon content results in adecrease in the strength of the anode and an increase in both itstendency to corrode and in its specific electrical resistance. If thecarbon content is too high, the carbon separates out in a graphiticform. I have obtained the best results with a carbon content slightly inexcess of the amount which can be combined, so that there is a smallamount of fine graphitic carbon, such as will give a grey surface to thefracture, but without any excess of graphitic carbon.

I have found that the alloys of cobalt and silicon are distinguishedfrom alloys of other more or less similar metals with silicon in theiravailability for use as electrodes. This distinction, and the advantagesof the cobalt-silicon alloys, are due in part, I believe, to the anodicproperties of the cobalt, that" is, to its tendency to be deposited onthe anode, which distinguishes cobalt from most other metals whichdeposit on the cathode. The advantageous proper.- ties of the cobaltalloys are further due, as I believe, to the peculiar characteristics ofthe cobalt-silicon alloys. Microphotographs of cobalt-silicon, alloyscontaining about 12 to 15 percent of silicon indicate that the siliconis in part present as such or in solid solution in the cobalt, while alarge part is present in the form of a eutectic made up of a solidsolution of cobalt silicide (CO Si) in the cobalt and perhaps also ofthe cobalt silicide itself. The microphotographs indicate that theresistance to corrosion may be largely due to the presence of thesilicon and of the cobalt silicide.

With anodes of cobalt-silicon alloys and copper cathodes I have found avoltage in dilute sulfuric acid of about 1.7 to 2.0 volts at a currentdensity of 20 amperes per square foot of anode surface and a spacing of1 inches between anode and cathode. I have furthermore found a maximumstrength against flexure to be obtained with a silicon content of about12 to 15%. For example, a flexure strength of around 6200 pounds persquare inch (unit beam 1 inch square, 12 inch span) has been possessedby electrodes of this silicon content. Both any material increase andany material decrease in the silicon content of the alloy seems todecrease the mechanical strength of the electrode, and in general, thegreatest strength is obtained at between 12 and 15% of silicon. In itsbreaking strength, the improved electrodes of the invention are to bedistinguished from electrodes of iron and silicon, where, for example, asimilar content of silicon gives an electrode with a flexure strength ofabout 1000 to 1500 pounds per square inch. The greater strength of thecobalt-silicon electrodes of the invention, as compared, for example,with iron silicon electrodes, enables a much thinner anode to beemployed without objectionable reduction in strength, so that less spaceis occupied thereby in the electrolytic tanks or cells. Any considerableincrease in the silicon content of the cobalt-silicon electrodes, asabove noted, tends to increase both the voltage and the brittleness.

I have obtained good results with a carbon content of about 1%, orbetween 0.5% and 1.2%, and with a silicon content of from 12 to 15%.Graphitic carbon, as above pointed out, is objectionable beyond acertain small amount, but inasmuch as cobalt will combine more readilythan iron with a small amount of carbon, it is possible to include sucha larger amount without an objectionable amount of graphitic carbonbeing present.

From investigations which I have made of microphotographs of electrodesembodying the principles herein disclosed, I believe the improvedelectrode of the invention owes its advantageous properties to the factthat it is composed, for the major part, of two constituents. The firstof these constituents is more or less soluble in the copper sulfateelectrolyte, but possesses good electrical conductivity. The secondconstituent is relatively insoluble in the electrolyte, but is not agood conductor of electricity. The aforementioned first constituentappears to be an alloy or a mixture of alloys of the various "metallicconstituents of the electrode, while the aforementioned secondconstituent appears to be a eutectic, probably silicide of cobalt. Itfurthermore appears from the microphotographs that the structure of theanode is made up of particles of the aforementioned first constituent(an alloy of good electrical conductivity but relatively soluble in theelectrolyte), which particles are more or less enclosed or envelopedwith a coating of the second constituent (the eutectic which isrelatively insoluble in the electrolyte but of poor electricalconductivity). The eutectic, accordingly, appears to provide a coatingfor the alloy particles which effectively serves to prevent theseparticles from going into solution at an objectionably high rate, but atthe same time this eutect1c coating is so shallow or narrow as not toobjectionably decrease the electrical conductivity of the electrode as awhole.

The cobalt-silicon anode of the invention is of special advantage insulfate electrolytes containing appreciable amounts of nitrates andchlorides. In such electrolytes lead anodes disintegrate rapidly. Leadanodes stand up more or less satisfactorily in sulfate electrolytes freeof nitrates or chlorides, but even in such electrolytes thecobalt-silicon anodeof the invention is sixperior to lead anodes, sincethe anode of the invention possesses a higher current efficiency than alead anode and stands up better in all electrolytes including those forwhich lead is adapted.

I have found the improved electrode of the invention of particular valuewhen employed as an anode in the electro-deposition of copper from suchsolutions as are obtained upon leaching Chuquicamata copper ores. Thiselectrolyte contains primarily copper sulfate, sulfuric acid, and anumber of other salts among which are included alkali nitrates,sulfates, chlorides and iron sulfates. In addition, the electrolyte maycontain small quantities of aluminum, calcium. magnesium and otassiumsulfates.

With an anode of t e preferred compo sition hereinbefore mentioned, Ihave found that the loss in electrodes of this character at 20 C. and at20 amperes per square foot of anode surface, is approximately 0.5 poundsper one hundred pounds of copper deposited, and that the voltage fromanode to cathode at this temperature is about 1.9

volts. I have found that higher temperatures give lower corrosionlosses, which is.in contradistinction to the behavior of ferrosiliconanodes.

I The manganese included in the improved electrode serves the purpose ofa depolarizer,

In an acid sulfate electrolyte at a tempera- --tically absent andinstead there is obtained a heavy deposit of manganic oxide on thesurface of the anode. In both cases, however, manganese dioxide isprecipitated or deposited on the anode, but in the case of the warm orheated solution, the deposit of manganese dioxide is more adherent andthere is practically no loss of manganese in the solution. This depositof manganese dioxide, together with some cobalt oxide, on the anode actsas a depolarizer, as'will be well understood by those skilled in theart, and insures the free discharge or liberation of oxygen gas from thesurface of the anode. Moreover, I have found that cobalt-silicon anodesmade up in accordance with the invention, but without manganese, have atendency to corrode at the solution surface line, and that this'tendencyis minimized by the addition of manganese to the alloy.

The addition of chromium or other chromium group metal to the electrodeacts to harden the manganese oxide film or deposit on the anode. Thus,the manganese dioxide film is more resistant. to abrasion in the case ofcobalt-silicon-manganese anodes containing chromium than it is in thecase of anodes of similar composition but without chromium, tungsten,molybdenum or nramum.

n will, therefore, be evident that while certain advantages of theinvention are obtained without the inclusion of either manganese or achromium group metal in the electrode that the presence of both of thesematerials is desirable, since the addition of these materials imparts tothe anode further desirable properties. Thus, I have found that theaddition of chromium to the anode greatly facilitates duplication of lowloss, low voltage anodes. In other words, I can obtain and readilyduplicate low loss, low voltage anodes more readily with chromium thanwithout chromium.

The proportions hereinbel'ore mentioned of the various ingredients of myimproved alloy generally represent What I now believe to be thepreferred from. of the invention. However, I wish it to be understoodthat these specific proportions mentioned may be somewhat varied withoutdeparting from the spirit of the invention. Thus, for example, I

have found that by increasing the silicon ciples of the invention intheir complete aspect should contain from about 7 to 20% silicon, fromabout 3 to manganese, from about 4 to 10% chromium or the equivalentamount of tungsten, molybdenum or uranium and the balance cobalt,(including the aforementioned relatively small percentage of carbon).

In the production of the improvedelectrode of the present invention, Imay employ cobalt with its normal impurities. including some smallpercentage of nickel, iron, manganese and carbon. I have obtained goodresults with cobalt containing around 4 to 7% of nickel and irontogether therein. In the production of the anodes. I may proceed bymelting the cobalt and adding charcoal thereto to increase its carboncontent, or by simultaneously reducing a mixed oxide of cobalt,manganese and chromium. (or other chromium group metal). I may then addthe silicon together with the manganese to the molten cobalt. but I havefound that the addition of the silicon to the cobalt results in aviolent evolution of heat, so that care should be taken to avoid theaddition of such large amounts of silicon as will result inobjectionable overheating. The silicon can be added gradually or ascarbide of silicon or it may be combined with a small amount of cobaltand the resulting alloy or mixture added to the remaining portion of thecobalt. This violent evolution of heat which takes place when thesilicon is added to cobalt is a further characteristic of thecobalt-silicon composition which distinguishes it from ironsiliconcompositions.

The electrode of the present invention, in addition to its improvedproperty of resisting anodic disintegration or corrosion, possesses indilute sulfuric acid a relatively low anodic potential or voltage. Inother words, the voltage between the anode and a copper cathode isrelatively low, being approximately from about 1.8 to about 2.0 volts at20 C. at an anode current density of about 20 amperes per square foot.This feature is of particular importance in the electrolytic productionof copper, since it is instrumental in determining the terminal voltagewhich must be applied to the electrolyzing tanks or cells. The cost ofelectrolytically precipitating copper from an electrolyte isproportional to the voltage which mustbe applied, and from thestandpoint of commercial economy, itis of the utmost importance that thesurface tension voltage of the anode be as low as practicable. Thecobalt-silicon electrode of the present invention, combining as it doesa relatively low surface tension voltage with very effective resistanceto anodic corrosion, makes a very durable, economical and satisfactoryanode in the electrolytic precipitation of copper.

I claim: 1. An electrode resistant to anodic disintegration and made upof an alloy containing cobalt in predominant amount and from 7 to 20percent of silicon.

2. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, from 7 to 20 percent ofsilicon and a depolarizing ingredient.

3. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, manganese and from 7 to20 percent of silicon.

4. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, from 7 to 20 percent ofsilicon, a depolarizing ingredient and a hardening agent.

5. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, manganese, chromium andfrom 7 to 20 percent of silicon.

6. An electrode resistant to anodic disintegration and made up of analloy containing cobalt, in predominant amount, manganese, chromium,from 7 to 20 percent of silicon and carbon.

7. An electrode resistant'to anodic disintegration and made up of analloy containing cobalt in predominant amount, manganese, chromium andabout 12 to 15 percent of silicon.

8. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, 7 to 20 percent ofsilicon and 3 to 45 percent of manganese.

9. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, 7 to 20 percent ofsilicon, 3 to 45 ercent of manganese and 4 to 10 percent of c romium.

10. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, 12 to 15 percent ofsilicon and 4 to 6 percent of manganese.

11. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, 12 to 15 percent ofsilicon, and 4 to 6 percent of chromium.

12. An electrode resistant to anodic disintegration and made up of analloy containing cobalt in predominant amount, 12 to 15 percent ofsilicon, 4 to 6 percent of manganese, and 4 to 6 percent of chromium.

13. An electrode resistant to anodic disin tegration and having a lowsolution tension or voltage made up of an alloy of cobalt with about 12to 15% of silicon, about 4 to 6% of manganese, about 4 to 6% of achromium group metal and sufficient carbon to supply a small amount ofgraphitic carbon to the alloy.

14:. An electrode resistant to anodic disintegration containing cobaltand silicon and structurally composed of two constituents,

the first of which is relatively soluble in copper sulfate electrolytesand of good electrical conductivity and the second of which more or lessenvelopes the first and is relatively insoluble in copper sulfateelectrolytes and of relatively low electrical conductivity.

15. An electrode resistant to anodic disin-s.

tegration containing cobalt, silicon, manganese, and chromium andstructurally composed of two constituents, the first of which isrelatively soluble in copper sulfate electrolytes and of good electricalconductivity and the second of which more or less en-" COLIN e. FINK.

